qemu/sparc-ss10: update defconfig to Linux 3.15.x

Update defconfig to 3.15, tested with Qemu 2.0.0.
Removed hint about framebuffer, as -display none is used.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>